In a UMTS (Universal Mobile Telecommunications System) network, long-term evolution (LTE) is under study for the purposes of further increasing high-speed data rates, providing low delay, and so on (non-patent literature 1). In LTE, as multiple access schemes, a scheme that is based on OFDMA (Orthogonal Frequency Division Multiple Access) is used in downlink channels (downlink), and a scheme that is based on SC-FDMA (Single Carrier Frequency Division Multiple Access) is used on in uplink channels (uplink).
In LTE, MIMO (Multi Input Multi Output), which achieves improved data rates (spectral efficiency) by transmitting and receiving data using a plurality of antennas, is defined. In MIMO, a plurality of transmitting/receiving antennas are provided in the transmitter/receiver, so that different information sequences are transmitted from different transmitting antennas at the same time. Meanwhile, on the receiving side, taking advantage of the fact that fading variation is produced differently between the transmitting/receiving antennas, information sequences that have been transmitted at the same time are separated and detected.
As MIMO transmission schemes, single-user MIMO (SU-MIMO), in which transmission information sequences for the same user are transmitted at the same time from different transmitting antennas, and multi-user MIMO (MU-MIMO), in which transmission information sequences for different users are transmitted at the same time from different transmitting antennas, have been proposed. In SU-MIMO and MU-MIMO, optimal PMIs (Precoding Matrix Indicators) to match the amount of phase and amplitude control (precoding weights) to be set in the antennas are selected from codebooks, and fed back to the transmitter as channel state information (CSI). On the transmitter side, each transmitting antenna is controlled based on the CSI fed back from the receiver, and transmission information sequences are transmitted.